Automatic transmission electronic gearshift control having altitude corrected shift criteria

ABSTRACT

An electronic control system for scheduling gearshifts in a four speed automatic transmission includes storing in electronic memory accessible to a microprocessor, six functions relating vehicle speed to throttle position, one function being related to each upshift and downshift. Gearshifts are made by probing computer memory with current values for throttle position and vehicle speed, and determining on the basis of the stored shift schedule whether an upshift or downshift is required. Upshift points are determined also on the basis of the maximum engine speed when a wide open throttle condition is detected. Ambient barometric pressure alters the vehicle speed and engine speed attained at high altitude in comparison to those speeds that result for the same throttle position at sea level. Therefore, shift points defined by the schedule on the basis of vehicle speed and throttle position, and shift points relates to wide open throttle conditions and engine speed, are corrected for altitude or barometric pressure changes from a reference barometric pressure at which the shift points are determined for the functions stored in computer memory.

BACKGROUND OF THE INVENTION

An electronic control system for scheduling gearshifts in a four speedautomatic transmission includes storing in electronic memory accessibleto a microprocessor, six functions relating vehicle speed to throttleposition, one function being related to each upshift and downshift.Gearshifts are made by probing computer memory with current values forthrottle position and vehicle speed, and determining on the basis of thestored shift schedule whether an upshift or downshift is required.Upshift points are determined also on the basis of the maximum enginespeed when a wide open throttle condition is detected. Ambientbarometric pressure alters the vehicle speed and engine speed attainedat high altitude in comparison to those speeds that result for the samethrottle position at sea level. Therefore, shift points defined by theschedule on the basis of vehicle speed and throttle position, and shiftpoints related to wide open throttle conditions and engine speed, arecorrected for altitude or barometric pressure changes from a referencebarometric pressure at which the shift points are determined for thefunctions stored in computer memory.

Wide open throttle shift points are corrected for altitude by comparingcurrent engine speed to the calculated engine speed resulting from thesum of a calibration constant stored in computer memory, which definethe engine speed above which an upshift is to occur at sea level, and aproduct formed by multiplying a barometric pressure interpolation factorand a predetermined engine speed of which the shift point at sea levelis reduced to account for altitude difference. This speed difference ismultiplied by the barometric interpolation factor and the product isadded to the sea level shift point engine speed to find the wide openthrottle engine speed corrected for altitude.

The second altitude correction is based on the stored schedule of shiftsrelating throttle position to vehicle speed. In this case, the shiftschedule is corrected by comparing current vehicle speed to an altitudecorrected vehicle speed involving a calibration constant vehicle speedwhere an upshift is made at sea level, a barometric pressure integrationfactor, a calibration constant stated in terms of vehicle speeddifference representing a correction of vehicle speed at sea level wherethe upshift is made, and the ratio of actual N/V to base N/V stored incomputer memory.

GENERAL DESCRIPTION OF THE INVENTION

The transmission of the present invention produces four forward speedratios and a reverse speed ratio. The third speed is a direct driveratio; the fourth speed is an overdrive ratio. The fourth or overdriveratio is achieved by holding the sun gear of a first simple planetarygear unit and by driving a second gear unit from the output of the firstgear unit while clutching together rotary elements of the secondplanetary gear unit so they rotate in unison. The three lowest forwardspeeds are produced by automatic shifts because a first overrunningclutch drivably connects rotary elements of the first gear unit withouttorque multiplication or speed reduction. The second and a third gearunit cooperate to produce torque multiplication through selectiveapplication of clutches and brakes, which drivably connect and holdelements of the later gear units.

In the lowest speed ratio produced by automatic shifts, a secondoverrunning clutch holds against rotation the carrier of the third gearunit. A third overrunning clutch completes a drivable connection betweenthe sun gears of the second and third gear units and a brake, therebyholding against rotation these sun gears to produce the second speedratio in the automatic mode.

Engine braking effect results by engaging a coast clutch in the first,second and third speed ratios when these ratios are selected manually.However, a band brake is applied during operation in the second speedmanual mode to replace the effect of the second overrunning clutch andintermediate brake, which are operative when drive is from the engine tothe wheels but inoperative when the drive is from the wheels to theengine. In this way, the inherently low torque capacity of the brakeband is required only when torque levels are low, i.e., during coastingoperation, but the intermediate brake and third overrunning clutch carrythe higher torques during drive operation.

A manual valve alternately connects a source of regulated line pressureto a forward drive passage and to a reverse drive passage. A shift valvealternately connects these passages to an input port of a coast clutchvalve in accordance with the state of a solenoid-operated valve. Acontrol port of the coast clutch shift valve is pressurized either froma manual valve, when the gear is selected manually by the vehicleoperator, or from a source of on-off pressure control by operation of asolenoid. In accordance with the control pressure, the coast clutchshift valve either connects its input to a line connected to the coastclutch or vents the input coast clutch to a drain passage in the shiftvalve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b are cross sections of a transmission according to thisinvention showing in the assembled condition a hydrokinetic torqueconverter, the clutches, brakes and gear units.

FIGS. 2a-2h are diagrams of the multiple-speed transmission showing inheavy lines the components that operate to produce each of the variousspeeds.

FIG. 3 is a table showing the engaged and disengaged states of hydraulicclutches and brakes and the driving and overrunning states of theoverrunning clutches for each speed and range in which the transmissioncan operate.

FIG. 4 is a table showing the states of solenoid-operated shift valves,a converter clutch valve and coast clutch valve for each speed and rangeof the transmission.

FIGS. 5a-5e show a hydraulic control system capable of engaging anddisengaging the hydraulic clutches and brakes of the transmission ofFIG. 1. The lines connecting the hydraulic components are labeledalphanumerically to indicate the hydraulic pressures in the lines foreach speed and range.

FIG. 6 is a schematic diagram of a drive system including a transmissionsuited for control by the system of this invention.

FIG. 7 is a block diagram of an electronic control system includinginput sensors, a microprocessor, its associated memory, data bus andoutput for operating solenoid valves located within the hydraulicsystem.

FIG. 8 is a graph illustrating the relationship between throttleposition and vehicle speed and their relationship to gear ratio upshiftsand downshifts made automatically by the transmission control.

FIG. 9 is a schematic diagram of certain software modules and dataacquisition statements executed during a background pass.

FIG. 10 is a cross section through an engine intake manifold showing theposition of a manifold pressure sensor and throttle plate.

FIGS. 11a and 11b are diagrams showing a technique for correcting shiftpoint speeds for barometric pressure.

FIGS. 12A-12C is a diagram showing logic for controlling a vehicle speedsensor shift module using the technique of FIG. 11.

FIG. 13 shows schematically a table of data stored in electronic memoryrepresenting factors applied to manifold pressure to produce inferredbarometric pressure.

FIG. 14 shows shift point speed correction data, at a reference altitudeand corresponding ambient barometric pressure, stored as fox functionsin electronic memory.

FIG. 15 is a graph of barometric pressure interpolation factor vs.inferred barometric pressure stored as a fox function in electronicmemory.

FIG. 16 is a diagram showing the change in engine speed and torqueconverter speed ratio over time during a 2-3 shift in which the torqueconverter is unlocked and relocked.

FIG. 17 is a graph, stored as a fox function in electronic memory,relating torque converter speed ratio unlock correction factor vs.throttle position.

FIG. 18 is a graph, stored as a fox function in electronic memory,relating torque converter speed ratio relock correction factor vs.throttle position.

FIGS. 19a and 19b are diagrams showing logic for controlling an upshiftconverter clutch module.

FIGS. 20a-20b are diagrams showing logic for controlling a shiftsolenoid state module.

DESCRIPTION OF THE PREFERRED EMBODIMENT 1. Gear Units, Clutches andBrakes

Referring first to FIG. 1, one end of an engine crankshaft 10 isdrivably connected through the transmission to the power output tailshaft 12, which is adapted to be connected to the vehicle tractionwheels through differential, driveline, and axle assemblies. The maintransmission housing 22 encloses simple planetary gear units 16, 18, 20.Transmission housing 22 is bolted at its left-hand periphery to thecylinder block of an internal combustion engine and, at its right-handend, to the left-hand end of tail shaft extension housing 24, whichsurrounds output shaft 12.

Transmission housing 22 encloses a hydrokinetic torque converter 26,which includes a bladed impeller 28, a bladed turbine 30 and a bladedstator 32. The impeller, the turbine and the stator are arranged influid flow relationship in a common toroidal circuit. The impellerincludes a housing connected drivably to drive plate 34, which is boltedto the end of crankshaft 10. Turbine 30 includes a turbine hub 36splined to turbine shaft 38. Impeller 28 is connected to impellerhousing 40, which is journalled for rotation on a portion 42 of a pumphousing, which closes converter housing 22. Pump housing 44 is bolted tohousing 22 and encloses gear elements of a positive fixed displacementpump 46, which serves as a pressure source for the control valve systemto be described with reference to FIGS. 5a-5e. A stator sleeve shaft 48extends from the pump housing 44 and supports the inner race 50 of aone-way clutch 52 whose outer race supports stator 32.

A torque converter lockup clutch 54 is splined at 56 to the turbine hub36 and carries a friction surface 58, located at its radially outer end,to drivably engage the torque converter cover 61, welded to the impellerhousing. Lockup clutch 54 is closed, locked, applied or engaged tocomplete a mechanical connection between the impeller and turbine whenpressurized hydraulic fluid, contained in the torque converter casing,forces friction surface 58 against the housing. The torque converter isopened, unlocked, released or disengaged so that a hydrodynamic drivingconnection exists between the impeller and turbine when pressurizedhydraulic fluid is supplied through passage 63 between converter cover61 and friction surface 58 of the lockup clutch to disengage thesesurfaces.

Turbine shaft 38 is splined at 58 to the carrier 60 of the firstplanetary gearset 16, which includes sun gear 62, a set of planetarypinions 64 rotatably supported on carrier 60 and ring gear 66. Sun gear62 is drivably connected to a member 70 that is common to a coast clutch72 and an overdrive brake 74. Ring gear 66 is drivably fixed to a drumportion 68 connected to intermediate shaft 76.

Overdrive brake 74 includes a set of clutch discs fixed to housing 22, aload block 78 fixed to housing 22, a set of clutch discs drivablyconnected to the outer surface of clutch member 70 and interposedbetween the discs affixed to the housing, a clutch piston 80displaceable hydraulically against the clutch disc assembly andhydraulic cylinder 82 containing piston 80, and a Belleville spring 84for returning piston 80 to the inactive position when hydraulic pressureis removed from cylinder 82.

Coast clutch 72 includes a set of clutch discs drivably connected to theinner surface of clutch member 70, a load block connected to the innersurface of clutch member 70, a second set of clutch discs drivably fixedto ring gear 66, piston 86 actuated hydraulically to engage the coastclutch disc sets, a hydraulic cylinder 88 within which piston 86 moves,and a Belleville spring 90 to return piston 86 to the disengagedposition when hydraulic pressure is removed from cylinder 88.

A first one-way clutch 92 has its outer race drivably connected to ringgear 66, its inner race drivably connected by a spline to cylinder 88and to sun gear 62 and a driving member located in the annulus betweenthe inner and outer races for producing a one-way driving connectiontherebetween. A second one-way clutch 94 is located between intermediatebrake 96 and direct clutch 98. One-way clutch 94 includes an outer racethat carries a set of brake discs for the intermediate brake 96, aninner race drivably fixed to drum 100, and a driving member located inthe annular region between the inner and outer races for producing aone-way drive connection therebetween.

Intermediate brake 96 includes a second set of brake discs fixed tohousing 22, a load block fixed to the housing, a piston 101 actuatedhydraulically to force the brake disc sets into drivable relationshipagainst the load block, hydraulic cylinder 83 within which piston 101moves and a Belleville spring.

Drum 100 is stopped and held against the transmission casing through theaction of an intermediate brake band 102 actuated by a hydraulicintermediate servo. Direct clutch 98 operates to produce a driveconnection between drum 100 and clutch member 104. The direct clutchincludes a first set of clutch discs splined to the inner surface ofdrum 100 and a second set of clutch discs connected to clutch member104, and interposed between successive members of the first clutch discset. A piston 106 moves within a hydraulic cylinder to force the clutchdisc sets into drivable connection against the load block that iscarried on the inner surface of the drum 100. Piston 106 moves withinthe hydraulic cylinder defined by drum 100 and is restored to itsdisengaged position through operation of a coil compression spring 108.

Forward clutch 110 operates to produce a driving connection betweenclutch member 104 and the ring gear 112 of the second planetary gearset18. This gearset includes a sun gear 114, a set of planetary pinions 116in continual meshing engagement with sun gear 114 and ring gear 112,rotatably supported on a carrier 118 which is drivably connected byspline 120 to the tail shaft 12.

Forward clutch 110 includes a first set of clutch discs drivablyconnected to the inner surface of clutch member 104 and a second set ofclutch discs, each interposed with discs of the first set, drivablyconnected to the outer surface of ring gear 112. Piston 122 ishydraulically actuated for movement within the cylinder defined byclutch member 104 to force the clutch discs into a drivable connection.Belleville spring 124 returns piston 122 to the disengaged position whenhydraulic pressure is removed from the clutch cylinder.

The third planetary gearset 20 includes sun gear 126 formed integrallywith sun gear 114, ring gear 128 connected by spline 130 to tail shaft12, a set of planet pinions 132 rotatably supported on carrier 134,which is drivably connected to a first set of brake discs of thelow-and-reverse brake 136. A second set of brake discs of brake 136 isfixed to transmission casing 22; each disc of the second set isinterposed between successive discs of the first disc set of brake 136.Brake piston 138 is actuated hydraulically when cylinder 140 ispressurized to force the piston against the first and second brake discsets and to produce a drivable connection therebetween against theeffect of the return spring 142, which forces piston 138 to the brakedisengaged position when cylinder 140 is vented. Load block 144, fixedto the transmission casing reacts the force applied by piston 138 to thedisc brake sets.

A third one-way clutch 146 includes an outer race pinned to carrier 134,an inner race 150 bolted to the transmission casing 22, and a drivingmember located in the annular region between the inner and outer racesto produce a one-way drive connection between carrier 134 and thecasing.

The transmission produces four forward gear ratios and a reverse gear.The three lowest of the forward gear ratios is produced bothautomatically and by manual operation of the gear selector lever by thevehicle operator. The third forward gear ratio directly connects theengine crankshaft 10 to tail shaft 12, and the fourth forward ratio isan overdrive ratio. When the gear selection is made manually by thevehicle operator, the three lowest forward gear ratios and the reversedrive involve the engagement of coast clutch 72, and through itsoperation, the engine braking effect is transmitted through thetransmission to the tail shaft 12. FIG. 3 shows engaged and releaseconditions of the clutches and brakes and driving and overrunningconditions of the one-way clutches for each of the gears and ranges ofthe transmission.

The gear selector lever includes a PRND21 switch, which produces anelectrical signal, preferably a voltage, whose magnitudes represent eachof the PRND21 positions. The gear selector and the manual valve itcontrols can be moved among the following alphanumeric positions fromleftmost to rightmost: P for park, R for reverse, N for neutral, D foroverdrive, 2 for manually selected second gear, and 1 for manuallyselected first gear. When the gear selector is in the D position and anoverdrive cancel button is depressed, a mechanically selected conditioncalled "drive" range, the transmission will produce only the threelowest gears. When the button is released, and the selector is in the ODposition, a condition called "overdrive" range, the transmission canproduce four forward gears. When the gear selector is moved to themanual 1 or 2 positions, the transmission produces only the first orsecond gear ratios, respectively.

Coast clutch 72 produces engine braking in third gear when the gearselector is in "drive". Otherwise, the transmission would freewheel inthird gear while the vehicle is coasting. When overdrive range isselected, coast clutch 72 is disengaged hydraulically but engine brakingresults in fourth gear through operation of overdrive brake 74. Whenmanual 2 and manual 1 are selected, the coast clutch is appliedhydraulically through operation of a coast clutch shift valve 302;whereas, when drive is selected, the coast clutch shift valve isactuated through operation of a solenoid-actuated coast clutch valvecontrolled by programmed logic. A manually initiated shift from fourthgear to third gear or second gear causes a short delay to allowoverdrive clutch 74 to release fully before coast clutch 72 engages.

To prevent intermediate band 102 from absorbing excessive drivelineenergy in the manual 2 and manual 1 ranges, application of band 102 isdelayed until the coast clutch engagement is inferred by expiration of ashift-in-progress timer.

The torque flow in each gear and range is described next with referenceto FIGS. 2a-2h.

First Gear-Overdrive and Drive Ranges--FIG. 2a

Low speed forward drive acceleration in the automatic mode is obtainedby engaging forward clutch 110. Torque then is delivered from turbineshaft 38 to carrier 60 of the first gearset 16. One-way clutch 92drivably connects ring gear 66 and sun gear 62 so that the entiregearset 16 turns as a unit and drives intermediate shaft 76. Torque isthen delivered from intermediate shaft 76 to the ring gear 112 throughengaged forward clutch 110, thus imparting a driving torque to carrier118 and the power output shaft 12. The reaction torque on sun gears 114,126 is in a reverse direction. This causes a forward driving torque onring gear 128, which is transferred to the output shaft 12 becausecarrier 134 acts as a reaction member. Carrier 134 is held againstrotation in this instance by overrunning brake 146.

In coasting operation, i.e. when torque flow is from output shaft 12toward shaft 38, OWB 146 overruns so that there is no torque path to thetorque converter.

First Gear Manual or 1 Range--FIG. 2e

The vehicle operator selects low speed operation manually by moving thegear selector lever to the 1 position. In this range, forward clutch110, reverse-low brake 136 and coast clutch 72 are engaged, butconverter lockup clutch 54 is always disengaged. Clutch 72 connects ringgear 66 and sun gear 62, so gearset 16 again turns as a unit and drivesshaft 76. Shaft 76 drives clutch 110, which drives ring gear 112 andcarrier 118. Brake 136 provides the reaction by holding carrier 134against rotation.

In coasting operation, the torque flow is from shaft 12 to shaft 76. Adrive connection to engine shaft 10 for engine braking effect iscompleted from shaft 76 by coast clutch 72 and torque converter 26.Clutch 72 is applied with the logic of the hydraulic circuit of FIGS.5a-5e.

Second Gear-Overdrive and Drive Ranges--FIG. 2b

Second speed ratio acceleration is achieved automatically by maintainingthe first gear status of the friction elements and by engagingintermediate brake 96. This holds sun gears 114, 126 against rotationbecause overrunning clutch 94 drivably connects brake 96 to drum 100.Powerflow from the engine to ring gear 112 is the same as that for thefirst speed overdrive and drive ranges. Planet pinions 116 are driven byring gear 112 and rotate with carrier 118 about sun gear 114. Ring gear112 continues to act as a power input element and carrier 118 continuesto drive the output shaft 12. Overrunning brake 146 free wheels so thatall of the torque multiplication is accomplished by gearset 18.

During coasting, shaft 12 drives carrier 118 and pinion 116. Ring gear112 and clutch 110 rotating at engine speed cause OWC 94 to free wheelin the coast direction, so the torque path ends there.

Second Gear Manual or 2 Range--FIG. 2f

In the manually selected second speed, the following friction elementsare engaged: coast clutch 72, intermediate brake 96, forward clutch 110and intermediate band 102. In drive operation, clutch 72 connects ringgear 66 and sun gear 62, so gearset 16 turns as a unit and drives shaft76. Shaft 76 drives ring gear 112 through clutch 110. Overrunning clutch94 drivably connects sun gears 114, 126 to intermediate brake 96, whichholds sun gear 114; therefore, pinions 116 are driven by ring gear 112and rotate with carrier 118 about sun gear 114. Brake 96 is engagedbefore band 102 is applied, as will be explained below, so full enginetorque is not carried solely by band 102 but is stored with brake 96.

In coasting operation, clutch 94 overruns and shaft 12 drives carrier118 and pinions 116 about sun gear 114, which is held by band 102. Ringgear 112 drives shaft 76 and ring gear 66 through forward clutch 110.Gearset 16 turns as a unit because coast clutch 72 connects ring gear 66to sun gear 62. Therefore, pinions 64 and carrier 60 drive shaft 38,which is connected by the converter 26, or by converter clutch 54, toengine shaft 10.

Third Gear-Overdrive Range--FIG. 2c

While accelerating in the overdrive range, third gear ratio results bymaintaining forward clutch 110 and intermediate brake 96 engaged and byengaging direct clutch 98. When the engine drives output shaft 12,overrunning brake 146 and overrunning clutch 94 freewheel, but one-wayclutch 92 drives. Shaft 76 and input shaft 38 turn at the same speed.One-way clutch 92 drivably connects ring gear 66 and sun gear 62 so thatturbine shaft 38 is drivably connected by the first gearset 16 tointermediate shaft 76. Direct clutch 98 and forward clutch 110 drivablyconnect ring gear 112, sun gears 114, 126 and intermediate shaft 76,which rotate as a unit. Planet pinion set 116, carrier 118 and outputshaft 12 are driven at the speed of the turbine shaft because of theconnection between ring gear 112 and sun gear 114. Overrunning brake 146free wheels. When the vehicle coasts, OWC 92 freewheels; therefore, ringgear 66 and sun gear 62 are disconnected and no engine braking effectoccurs.

Third Gear Manual or Drive Range--FIG. 2g

When the overdrive cancel switch is closed on the gear selector to placethe transmission in the drive range, the friction elements operate asthey do to produce third gear in the overdrive range except that coastclutch 72 is engaged. The transmission produces a direct connectionbetween input shaft 38 and output shaft 12, as in third gear overdrive,except that clutch 72 connects ring gear 66 and sun gear 62 instead ofOWC 92.

When the vehicle coasts, clutch 72 remains engaged, gearset 16 drivablyconnects shafts 76 and 38, and the torque converter connects shaft 38 toengine shaft 10.

Fourth Gear Overdrive Range--FIG. 2d

The fourth gear ratio is achieved by maintaining forward clutch 110,direct clutch 98 and intermediate brake 96 engaged and by engagingoverdrive brake 74. Sun gear 62 of gearset 16 is held against rotationby brake 74 and one-way clutch 92 freewheels due to the engagement ofoverdrive brake. In this instance, ring gear 66 and intermediate shaft76 are driven at a higher speed than turbine shaft 38 and carrier 60.Gearsets 18 and 20 are disposed in the same condition as they were forthe third gear ratio in the automatic mode; therefore, the speed of theoutput shaft 12 is the same as the speed of the intermediate shaft 76.

In coasting operation, overdrive brake 74 remains engaged and the torquepath from output shaft 12 to engine shaft 10 is completed by gearset 16and the torque converter. Engine braking is therefore operative.

Reverse Gear--FIG. 2h

Reverse drive is achieved by releasing intermediate brake 96, forwardclutch 110 and overdrive brake 74 and by applying low and reverse brake136, direct clutch 98, and coast clutch 72. With the friction elementsso disposed, one-way clutch 94 free wheels, one-way clutch 92 isinactive and one-way brake 146 is inactive. Coast clutch 72 drivablyconnects sun gear 62 and ring gear 66 of the first gearset 16 so thatturbine PG,17 torque is delivered from shaft 38 directly to sun gears114, 126. With carrier 134 acting as a reaction point, ring gear 128 andpower output shaft 12 are driven in a reverse direction.

The transmission will produce upshifts and downshifts among the threelowest gear ratios in the drive range, and among all four gear ratios inthe overdrive range. Engine braking occurs in the highest gear availablein each range, i.e., 1, 2, drive and overdrive. The schedule of FIG. 4shows the status of the coast clutch solenoid in each gear of each rangeand the availability of engine braking.

2. Hydraulic Circuit

FIGS. 5a through 5e show the hydraulic control valve system thatcontrols application and release of the hydraulic clutches and brakes ofthe change-speed gear box of FIGS. 1 and 2. The various passages arepressurized in accordance with selected positions of a manual valve 160,moved manually by the vehicle operator among six positions p, R, N, OD,2 and 1, and states of certain solenoid-operated valves as determined bymicroprocessor execution of control algorithms.

Fluid required for the operation of the hydraulic control valve systemis supplied at the output of a hydraulic pump, which is supplied fromthe sump or reservoir of the transmission through a filter or from areturn line connected to the inlet of the pump. The pump may be a fixeddisplacement pump that produces a flow rate proportional to its speed.

Line pressure Regulation

Line pressure magnitude is controlled by main regulator valve 162 shownin FIG. 5a. This valve operates in response to control pressure carriedin line 164 from TV pressure valve 166. Valve 166 is connected bypassages 168 and 170 from regulated line pressure produced by mainregulator valve 162. A variable force solenoid 172 regulates TV pressureby having applied across its winding an electrical voltage duty cycle inaccordance with the control of the microprocessor output. Hydraulicpressure having a magnitude between 5 psi and 85 psi produced by valve166 is applied to the end of line regulator valve 162. When there isdemand for a high volume of fluid at line pressure, spool 172 movesdownward due to TV pressure operating against the effect of a set ofcoil springs 174, closes the return line to the suction side of thepump, and closes torque converter charge line 176. Then substantiallythe entire volumetric flow of the pump is carried in passage 170.

The magnitude of pressure in line 170 is a result of upwardly directeddifferential pressure on the lower end of spool 172 acting against thespring forces and a TV pressure force directed downward on the spool.When line pressure is high in relation to TV pressure, spool 172 movesupward and opens the feedback line to the suction side of the pump.Before this occurs, however, line 176 to converter regulator valve 178is opened. Thus, line pressure is regulated by balancing the springforces and TV pressure against line pressure in passage 170.

When manual valve 160 is moved to the 1 and R positions, line pressureis carried in passages 180, 182 to a differential pressure area of themain regulator valve. The pressure developed on the differential areaoperates to force spool 172 downward so that line pressure is higherwhen the reverse and 1 ranges are selected than for any of the othersettings of the gear selector and manual valve. Higher line pressure inthese ranges increases the torque capacity of the clutches and brakesengaged to produce the first gear and reverse drive while engine torqueis near its peak magnitude.

Solenoid-Operated Valves

Passage 170 carries line pressure to solenoid regulator valve 184, whichproduces a regulated solenoid feed pressure carried in passage 186 tofirst and second solenoid-operated shift valves 188, 190, a converterclutch solenoid-operated valve 192, and coast clutch solenoid-operatedfeed valve 194. Regulator valve 184 maintains the output in line 186 atapproximately 50 psi by balancing spring force applied to the spoolagainst an opposing line pressure force on the spool end resulting fromfeedback output.

Valves 188, 190, 192 and 194 are on-off valves that alternately connectand disconnect line 186 and output lines 196, 198, 200 and 202,respectively. The solenoids that operate these valves are controlled bythe output of the microprocessor, which selectively energizes anddeenergizes the solenoids in accordance with the result of executingelectronically stored control algorithms accessible to themicroprocessor. For example, when the solenoid of valve 188 isdeenergized, line 196 is vented by being connected to the low pressuresump. But when the solenoid is energized, solenoid feedline 186 isconnected to line 196. Similarly, valves 190, 192 and 194 either connectsolenoid feedline 186 to lines 198, 200, 202 or vent these lines inaccordance with the state of the corresponding solenoids.

Converter Clutch

Converter clutch 54 is engaged to lock torque converter 26 bypressurizing line 204 and venting line 206. The converter clutch isdisengaged and the torque converter opened when line 206 is pressurizedand line 204 is vented. Converter clutch control valve 208 moves upwardwithin the valve body due to a force on spool 210 resulting fromconverter clutch solenoid pressure carried in line 200. Valve 208 isforced downward by the helical spring and a pressure force resultingfrom 1-R pressure carried in line 180 to the upper end of spool 210.Also, control valve 208 is supplied through line 212 with regulatedconverter feed pressure from converter regulator valve 178, whichregulates converter feed pressure in line 212 by sensing the pressure inline 212 and throttling converter charge pressure in line 176. Whenconverter clutch solenoid valve 192 is energized, line 200 ispressurized, and spool 210 moves upward against the force of the springto connect lines 212 and 204. When this occurs, line 206 is connected byvalve 208 to vent port 214 and converter clutch 54 is engaged.

When solenoid valve 192 is deenergized, line 200 is vented causing spool210 to move downward, closing the connection between lines 212 and 204,closing the connection of line 206 to vent 214, and opening a connectionbetween lines 212 and 206. This vents line 204 through valve 208 and ahydraulic fluid cooler to the sump of the transmission. This actionopens the torque converter by disengaging the mechanical connection ofimpeller 28 and turbine 30 made through clutch 54. The 1-R pressure, inaddition to increasing line pressure for a given TV pressure, asdescribed with respect to the operation of valve 162, also operates toopen the torque converter if solenoid valve 192 remains open while thegear selector is moved to the 1 or R positions, perhaps due to failureof the solenoid that operates valve 192, a short circuit or otherelectrical fault. This 1-R pressure assures the torque converter will beopen if the gear selector is located in the R and 1 positions so thatthe torque multiplication effect of the converter is available tomaximize torque to output shaft 12. Converter regulator valve 178 limitstorque converter feed pressure to approximately 110 psi.

Line modulator valve 220 is connected to regulated line pressure bypassages 170, 168 and 222, and to TV pressure by passages 164 and 224.

Automatic Forward Drive

Regardless of whether the OD cancel button is depressed on the gearselector mechanism, whenever manual valve 160 is moved to the ODposition, the position shown in FIG. 5d, regulated line pressure inpassage 168 is connected through valve 160 to passage 226. Forwardclutch 110 is continually connected to regulated line pressure throughpassage 226, orifice 342 and passage 242; provided the manual valve isin a forward drive position. First gear results for automatic shiftingwhen the forward clutch alone is engaged in this way.

In the OD range and with the transmission operating in first gear, firstsolenoid shift valve 188 directs SOL1 pressure to 1-2 shift valve 228through passage 196 and to 2-3 shift valve 232 through passage 244, butsecond solenoid shift valve 190 is exhausted. Therefore, shift valves228 and 232 are moved by SOL1 pressure to the rightward extremity,closing line pressure passages 227 and 230, respectively. In this wayonly forward clutch 110 is pressurized and first gear operation results.

An upshift to second gear occurs while first solenoid shift valve 188remains open and after second solenoid shift valve 190 is opened. Valve190 directs SOL2 pressure through passage 198 to the end of 3-4 shiftvalve 236 and to manual timing valve 306. Passage 198 also directs SOL2pressure to shuttle valve 246. If passage 372 is not pressurized, valve246 directs SOL2 pressure to manual transition valve 250. If L/R clutchpressure passage 370 is not pressurized, transition valve 250 directsSOL2 pressure to the spring end of 1-2 shift valve 228. The 1-2 shiftvalve is moved leftward by SOL2 pressure, thereby opening the connectionbetween passages 227 and 254, through which regulated line pressure iscarried to intermediate brake accumulator 256.

Line Modulator and Accumulator

Line modulator valve 220 and accumulator 256 work cooperatively tosupply pressurized fluid to intermediate brake 96 thereby engagingsecond gear. Line modulator valve 220 supplies TVLM pressure tointermediate brake accumulator 256, overdrive clutch accumulator 260,and direct clutch accumulator 262. Each accumulator is shown with itsplunger located as it is prior to an upshift and filled with hydraulicfluid supplied from valve 220.

Valve 258, located immediately above accumulator 256, balances thespring force against intermediate brake pressure and moves upwardconnecting passages 254, 261. The upper end of accumulator 256 is filledthrough orifice 264. The orifice establishes a constant pressure dropand flow rate into the upper end of the accumulator cylinder and movesthe plunger downward at a rate consistent with the flow rate throughorifice 264 against the force of the springs within the accumulator andTVLM pressure within the accumulator below the plunger. In this way, thepressure in passage 261 rises linearly and rapidly when valve 258 firstopens; thereafter, pressure in brake 96 increases linearly as timeincreases at a lower rate determined by the flow rate through orifice264 and the spring constant of the springs within the accumulator. Also,pressure in brake 96 has a magnitude for each unit of elapsed time thatvaries with TV pressure, as is explained below.

The output of valve 220 is TVLM pressure supplied to the space withineach of the accumulators below the plungers. Valve 266, located at thetop of the bore of line modulator valve 220, regulates by balancing TVLMpressure against the force of the inner isolator spring 268, a shortspring having a relatively high spring rate that prevents contactbetween spools 270 and 266 when spring 268 is fully closed. When TVpressure, carried in passages 164, 224 from VFS valve 166, isapproximately 6 psi or lower, spool 270 is held by the outer spring atthe lower end of the valve bore, and spring 268 does not touch spool266. In this range of TV pressure, passage 272 is vented through port269 because feedback TVLM pressure will have forced spool 266 downwardclosing communication between passages 222 and 272. When TV pressurerises above 6 psi, valve 270 rises off its seat against the effect ofthe outer spring. Spring 268 causes valve 266 to regulate because itmoves valve 266 upward causing TVLM pressure to rise by one unit foreach two unit increase of TV pressure above 6 psi. In this way, linepressure is modulated according to the magnitude of TV pressure producedby VFS valve 166 in accordance with the control of the microprocessor.

Accordingly, the pressures produced by accumulators 256, 260, 262increase linearly with time after the initial rapid rise in their outputpressures following their being pressurized from passages 254, 278 and280, respectively. The pressures produced by the accumulators are higherat a given time after their linear increase begins if TV pressure ishigh, and lower at that time if TV pressure is low, because TVLMpressure varies linearly with TV pressure above 6 psi.

During the upshift, TVLM pressure in line 272 remains substantiallyconstant because fluid forced from below the accumulator plunger brieflyand slightly raises the pressure force at the head of valve 266, andopens the connection between line 272 and the vent 269 in modulatorvalve 220. Then the pressure in line 272 falls and the opening to vent269 closes. This lost fluid is returned to the accumulator through line222 while the accumulator is being recharged. When the intermediatebrake is to be disengaged, for example, during a 2-1 downshift, theprocess for activating the accumulator is substantially reversed fromthat of the upshift. The 2-1 downshift occurs when line 254 is vented at384 through 1-2 shift valve 228 due to the presence of SOL1 pressure andthe absence of SOL2 pressure at that shift valve. Flow from the spaceabove the plunger of accumulator 266 through orifice 275 and theconstant spring rate of the accumulator springs again controls the rateat which the plunger rises within its chamber and the rate at which theaccumulator cylinder below the plunger is filled with fluid from line222 and line modulator valve 220. As the accumulator is being recharged,fluid within the accumulator cylinder above the plunger flows throughone-way check valve 274, and passages 263, 254. Check valve 277 directsfluid through 2-1 downshift orifice, and, the fluid is vented through1-2 shift valve 228. Likewise, intermediate brake 96 is vented throughpassages 261, 254, the 2-1 downshift orifice and shift valve 228.

Intermediate brake 96 remains engaged for third gear and fourth gearduring automatic operation because 1-2 shift valve 228 connects passages227 and 254 for any combination of states of solenoid valves 188, 190except the first gear states.

Overdrive clutch accumulator 260 works, as accumulator 256 does, topressurize and vent overdrive clutch 74 through passage 276 during a 3-4upshift and 4-3 downshift. These upshifts and downshifts are initiatedby selectively pressurizing and venting passage 278 through 3-4 shiftvalve 236, as described below.

An automatic upshift from second gear to third gear occurs after firstsolenoid shift valve 188 is closed by deenergizing its solenoid, andmaintaining second solenoid valve 190 open, according to the schedule ofFIG. 4. Line pressure continues to be directed by manual valve 160through passages 226, 230 to 2-3 shift valve 232. Because of the absenceof SOL1 pressure, valve 232 moves to the position of FIG. 5e. This opensline pressure to passage 280 through which control valve 282 at the endof direct clutch accumulator 262 is pressurized. Direct clutch 98 isthereby pressurized rapidly over a first, short portion of itsengagement period, during which the clearances among the variouscomponents of the clutch are taken up. Thereafter, clutch 98 ispressurized at a linearly increasing pressure controlled by themagnitude of TVLM, the rate of flow through orifice 284, and the springconstant of accumulator 262, as has been previously described withrespect to accumulator 256, until the clutch is fully engaged. Clutch 98remains engaged during third gear and fourth gear operation because SOL1pressure is absent; therefore, 2-3 shift valve 232 maintains open theconnection between line pressure and accumulator valve 282.

An automatic 3-2 downshift occurs when solenoid valves 188 and 190 areboth on. Then SOL1 pressure forces 2-3 shift valve rightward so thatdirect clutch 98 is drained through passages 286, valves 282, passage280, orifice 283, shift valve 232, passage 290, 3-4 shift valve 236, andpassage 292 to sump through manual valve 160. This path to sump from thedirect clutch is continually open through the 3-4 shift valve 236regardless of the presence or absence of SOL2 pressure at valve 236.

An automatic upshift from third gear to fourth gear results whensolenoid valves 188 and 190 are both closed, whereby overdrive brake 74is engaged. When this occurs, 3-4 shift valve 236 is moved by its springto the position shown in FIG. 5d, whereby line pressure from the manualvalve is directed by passage 234 through the shift valve to passage 278.Control valve 286 at the end of overdrive accumulator 260 is moved byits spring downward so that brake 74 is pressurized through passage 276rapidly during the first, short phase of engagement of the brake duringwhich clearances among the components of a brake are taken up.Thereafter, pressure in brake 74 rises linearly with time according tothe control of TVLM pressure, the flow rate of fluid through orifice 288and the spring constant of the accumulator, as has been described withrespect to accumulator 256.

An automatic downshift from fourth gear to third gear occurs when SOL 2pressure is applied to shift valve 236. This action moves the valverightward opening a connection through passage 278, valve 286, passage276 and brake 74 to the vent port at shift valve 236.

Reverse Gear

When manual valve 160 is moved to the R position, line pressure inpassage 168 is directed to passages 180, through bypass loops 294, 295to passage 292, and passage 226 is closed to the source of linepressure. Thus, forward clutch 110 is disengaged. Solenoid valve 188 isopened to connect SRV passage 186 to SOL1 passage 196, but solenoidshift valve 190 is closed. SOL1 pressure is carried in passage 244 tothe end of 2-3 shift valve 232, and to the SOL1 port of 1-2 shift valve228.

Passage 180 is connected to line pressure both when the manual valve ismoved to the R position and to the 1 position. 1-R pressure forces spool210 of the converter clutch control valve 208 downward, therebydirecting regulated converter pressure through valve 208 and passage 206to open converter clutch 54. This action assures that, if SOL3 pressure,which is limited to 50 psi, remains on while the gear selector or manualvalve is in the 1 or R position, there is sufficient pressure to pushspool 210 downward and open the torque converter. In this way, thetorque converter is opened when 1 or R positions are selected so thatthe torque multiplication capacity of the torque converter is availableduring these high torque conditions. Passage 182 carries line pressurefrom valve 208 to the main regulator valve 162 when the gear selector isin the 1 and R positions. This forces spool 172 downward, closes returnto the pump inlet, and directs more pump output to passage 170.

Passage 300 and one-way check valves 299, 301 direct 1-R pressure alsoto the end of coast clutch shift valve 302. Check valve valve 299 andpassage 304 carry 1-R pressure from the manual valve to manual timingvalve 306.

Because SOL2 pressure is absent, 3-4 shift valve 236 is in the positionshown in FIG. 5d. Therefore, when the manual valve is moved to the Rposition, shift valve 236 connects line pressure in passage 292 topassages 290, 310 and 318. Check valve 312 directs R pressure throughorifice 314 to the end of low/reverse modular valve 316, where apressure force acting on the valve in opposition to its spring, opens Rpressure in passage 318 to low/reverse brake passage 320. Low/reversebrake 136 is the first friction element to become engaged in the processof producing reverse drive.

The 3-4 shift valve 236 also connects R pressure in passage 318 to coastclutch shift valve 302 through passage 322. Control pressure to coastclutch shift valve 302 is directed from passage 300 through the checkvalve 301 to passage 324. Valve 302 moves leftward against the effect ofits spring due to 1-R control pressure and completes the connection frompassage 322 to passage 326 and passage 330 to coast clutch 72, which isthe second friction element applied during reverse drive engagement.

Manual Shift Timing Valve

When the manual valve is in the R position, 1-2 shift valve 228 connectspassages 310 and 332 through check valve 370. Manual timing valve 306includes a piston 360, which is forced into contact with retaining plate363 by SRV pressure forwarded from solenoid regulator valve 184 andmaintained at a constant pressure by that valve. A second piston 330 isbiased by a spring into contact also with retainer plate 363. First andsecond inlet passages 360, 362 supply 1-R/MAN2 pressure to timer valve306 from passage 304. An orifice 364, located in passage 362, controlsthe flow rate through that passage and through valve 306 during aportion of its operation. Thereafter, when the valve opens, the higherpressure in passage 360 is directed to outlet passage 366.

In operation, first piston 360 is forced by SRV pressure into contactwith plate 363. Second piston 330 is forced by the spring into contactwith the plate against feedback pressure in passage 366, 368 tending tohold spool 330 rightward. This closes passage 360 but permits flowthrough orifice 364 and passage 366 to feedback passage 368. Ball checkvalve 370 and passage 332 carry R pressure from 1-2 shift valve 228 totiming valve 306, but check valve 370 closes passage 332 when it is at ahigher pressure than passage 310. Therefore, R pressure in passage 332is directed by valve 306 immediately without delay to passage 334because R pressure forces valve spool 330 rightward and opens thisconnection.

The space immediately adjacent both sides of the retainer plate ispressurized through feedback passage 368. Because of the differentialpressure across its ends, piston 360 immediately moves for a shortperiod away from the plate against SRV pressure until piston 360 seatson the valve body at the left-hand extremity. After this occurs,pressure rises quickly in the annulus, within which the retainer plateis located, and piston 330 moves rightward, subject to the flow rateacross orifice 364, against the spring force until it becomes seated atthe right-hand end of the valve chamber. In this position, feedbackpassage 368 is open to passage 334, through valve 306 and passage 360 isopen also to passage 334 through passages 366 and 368. The operation ofthe manual timing valve, therefore, delays the occurrence of Delayed1-R/MAN2 pressure at 2-3 shift valve 232 by the period while piston 360moves from the right-hand end of its chamber to the left-hand end plusthe period while spool 330 moves rightward from plate 363 until valve306 opens.

Valve 306 assures that whenever the vehicle operator moves manual valve160 to the 1, 2 positions, a delay occurs before pressure from themanual valve is present at 2-3 shift valve 232. This produces a shortdelay, one or two seconds, before a downshift from third or fourth gearcan be made into second gear. For example, when a 4-2 downshift iscommanded by the vehicle operator by a manual shift to the 2 position athigh speed, the transmission will dwell for a period, the periodrequired for the manual timing valve to produce MAN2 pressure in thirdgear, before the downshift to the second gear is completed. In thirdgear drive range, coast clutch engagement produces the engine brakingeffect, whereas in second gear manual operation, intermediate band 102and servo 96 produce the engine braking effect. Torque capacity of theband and servo are much lower than torque capacity of the coast clutch.By avoiding an immediate high speed 4-2 downshift, torque loads areeventually placed on band 102 are lower than otherwise they would be.Similarly, high speed downshifts into first gear are delayed to avoidthe sensation of an abrupt downshift.

However, SOL2 pressure at the end of timing valve 306 increases thedelay, or the absence of SOL2 pressure prevents entirely any delay inpressure being output from valve 306, depending on the magnitude of1-R/MAN2 pressure compared to SOL2 pressure, the force developed on thespring of valve 306, and the occurrence of SOL2 pressure.

When manual timing valve 330 is positioned at the right-hand end,pressure in passage 332 is directed as R pressure to passages 334, 336to ports of the 2-3 shift valve 232. Also, R pressure is present at 2-3shift valve 232 at the end of passage 290. As a result of pressure inpassage 334, a differential pressure is developed on the spool of shiftvalve 232, which, regardless of the effect of SOL1 pressure at the endof the spool, forces the spool rightward against the effect of thespring to connect passage 290 to passage 280. Control valve 282 at theend of the direct clutch accumulator 262 is pressurized through passage280 and check valve 338. In this way, application of direct clutch 98 isboth controlled to rise linearly with time through operation ofaccumulator 262 and delayed with respect to engagement of low reversebrake 136 and coast clutch 72. When the direct clutch is fully engaged,reverse drive is completed.

Forward Clutch Valve

R pressure from manual valve 160 is directed by passages 292, 310 alsoto the reverse port of the forward clutch valve 240. TV pressure also isdirected through passage 340 from variable force solenoid valve 166 tovalve 240. When TV pressure is high, as when transmission fluid is coldor the accelerator pedal is depressed substantially, valve 240 connectspassages 310 and 344. This action adds flow of hydraulic fluid throughvalve 240 to flow from accumulator 262.

If the manual valve is in the OD or D position, and throttle pressure ishigh, valve 240 moves leftward against the force of its spring and opensa connection between passage 238, which contains fluid at line pressurewhenever the manual valve is in the OD position, and passage 242 to theforward clutch. This action adds the flow of hydraulic fluid throughvalve 240 to the volume supplied through passage 226 and orifice 342during automatic operation in forward drive. Therefore, when ambienttemperature is low and the viscosity of the hydraulic fluid isrelatively high, TV pressure increases the flow to the forward clutchand to the direct clutch to produce forward drive and reverse driveoperation, respectively.

First Gear Manual

When first gear is produced manually by moving manual valve 160 to the 1position, the transmission operates in the first gear by engagingforward clutch 110, low-reverse brake 136 and coast clutch 72, openingfirst solenoid shift valve 188, and closing second solenoid shift valve190. In this position, the manual valve connects passages 168 and 180through bypass loops 294 and 295, but passages 292, 226 and 318 aredisconnected from line pressure passage 168. Converter lockup clutch 54is disengaged and the torque converter opens through operation of theconverter clutch control valve 208, main regulator valve 162 andconverter regulator valve 178, as was previously described withreference to reverse drive operation.

When manual timing valve 306 times out, passage 334 communicates Delayed1-R pressure to two ports of the 2-3 shift valve 232, which is movedrightward by the presence of SOL1 pressure at the lefthand end of thevalve. This action opens communication between passages 336, 350 to aport of the 1-2 shift valve 228. SOL1 pressure in passage 196 movesshift valve 228 rightward, thereby connecting passages 350 and 352.Low-reverse modulator valve 316 supplied with R/Manual 1 pressure inpassage 352, is moved leftward by its spring connecting passage 352 topassage 320, through which low reverse brake 136 is engaged.

When the manual valve 160 is in the 1 position, it directs line pressurefrom passage 168 through passage 226, orifice 342, and passage 242 tothe forward clutch 110.

The coast clutch is energized through the manual valve 160, whichdirects line pressure through passage 180, check valves 299, 301 andpassage 324 to coast clutch shift valve 302.

Line pressure directed by manual valve 160 through passages 226, 230 ispresent at a port of the 2-3 shift valve 232. The presence of SOL1pressure or Delayed 1-R pressure will have moved shift valve 232rightward, thereby closing vent line 356 and connecting lines 230 and358. The differential pressure on the spool of 3-4 shift valve 236produced by pressure in passage 358 opens a connection between linepassage 234 and coast clutch passage 322. Coast clutch shift valve 302moves leftward due to the presence of 1-R pressure at its righthand end,and connects passages 322 and 326 to coast clutch 72 through orifice 374and passage 330. Delayed 1-R pressure transmitted in passage 334 to 2-3shift valve 232 is also passed through valve 232, passage 350, 1-2 shiftvalve 228 and passage 352 to low-reverse modulator 316. Low-reversebrake 136 is pressurized from valve 316, as is described above.

Second Gear Manual

A manual shift to second gear results when the gear selector manualvalve 160 is moved to the 2 position and both shift solenoid valves 188and 190 are turned on. In this position, the manual valve connectspressure in passage 168 to passages 226, 372 and disconnects passages180, 292, 318 from line pressure. Forward clutch 110 is pressurized, asit is for each of the four forward gears, directly from the manual valvethrough passages 226, 242 and orifice 342.

The presence of SOL2 pressure at the end of 3-4 shift valve 236 movesthe valve rightward to open the connection between passage 234, whichreceives line pressure through passage 226, and passage 322, whichtransmits line pressure from shift valve 236 to coast clutch valve 302.Manual valve 160 directs MAN2 pressure through passages 372, directionvalve 299, passage 300, direction valve 301 and passage 324 to thecontrol end of the coast clutch valve. The presence of the controlpressure at valve 302 opens a connection between passages 322, 326 anddirects coast clutch pressure through orifice 374 and passage 330 tocoast clutch 72.

Whenever coast clutch solenoid valve 194 is on, SRV pressure isconnected through valve 194 to passage 202 and direction valve 301 ispressurized, thereby closing passage 300 and pressurizing the controlport of coast clutch valve 302 through passage 324. This action,therefore, engages the coast clutch by completing a connection betweenpassages 322 and 326 regardless of the state of the manual valve.

MAN2 pressure is directed from manual valve 160 through passage 372,direction valve 299 and passage 304 to passages 360 and 362, which leadto manual timing valve 306. When the delay period of the valve expires,MAN2 pressure is connected through the valve and passages 334, 336 tothe 2-3 shift valve 232. MAN2 pressure develops a differential pressurepresent at that shift valve, opens passage 230 to passage 358, which isclosed at 3-4 shift valve 236, and directs MAN2 pressure through line350 to 1-2 shift valve 228. The 1-2 manual transition valve 250, biasedupward by its spring because of the absence of low-reverse brakepressure in passage 370 and at its control port, directs MAN2 pressureto passage 252. MAN2 pressure adds to the effect of the spring at shiftvalve 228 and works in opposition to SOL1 pressure to move shift valve228 leftward, thereby closing the connection between passages 350, 352and opening a connection between passages 350, 380. MAN2 pressure isdirected through orifices 382, 383 to the intermediate servo 96.Orifices 382, 383 delay engagement of servo 97 so that intermediatebrake 96 is engaged shortly before servo 97, actuates band 102 and holdsdrum 100 against rotation. With the 1-2 shift valve so disposed, linepressure in passages 226, 227 and present at shift valve 228 isconnected by passage 254 to the control valve at the end of intermediateclutch accumulator 256, by means of which passage 260 and intermediatebrake 96 are pressurized in accordance with the technique describedabove. The delay in applying servo 97 and band 102 until after brake 96is applied assures that engine torque is not carried by band 100.

A manual downshift to first gear from second gear occurs after MAN2pressure is removed from the control end of the 1-2 shift valve. Thiscauses shift valve 228 to move rightward thereby closing the connectionbetween passages 350 and 380 to the intermediate servo 96, connectingpassages 350 and 352 to low-reverse brake 136 through the low reversemodulator valve 316, disconnecting passages 226 and 254, and connectingpassage 254 to vent port 384. In this way, intermediate brake 96 isvented and drained through accumulator control valve 258. The fluidabove the plunger of accumulator 256 passes through the 2-1 downshiftorifice near ball check valve 277 in passage 254 and eventually to vent384.

Third Gear Manual

When the manual valve is moved to the OD position and the drive buttonis depressed, the transmission will produce automatic shifts among thefirst three gears in the manner previously described with respect toautomatic operation. However, in this case, unlike overdrive operation,third gear has engine braking effect due to engagement of the coastclutch. Intermediate brake 96, direct clutch 98, and forward clutch 110are applied as described above with respect to overdrive operation. Toproduce third gear, second solenoid shift valve 190 is on and firstsolenoid shift valve 188 is off. The 3-4 shift valve 236, movedrightward by SOL2 pressure, opens a connection between passage 234 andcoast clutch pressure in passage 322.

Coast Clutch Shift Valve and Solenoid Valve

When a command is made for third gear operation and the manual valve isin the overdrive position with the drive range button depressed, coastclutch solenoid valve 194 is on and it directs SOL4 pressure throughpassage 202. Check valve 301 pressurizes the control port of coastclutch shift valve 302. This moves shift valve 302 leftward and connectscoast clutch pressure in passage 322 to passage 326, through which coastclutch 72 is engaged, whereby the transmission is disposed for operationin third gear with engine braking.

To upshift from manual third gear to fourth gear coast clutch 72 isdisengaged and overdrive clutch 74 is engaged. To disengage the coastclutch, 3-4 shift valve 236 moves leftward when SOL2 pressure isremoved, thereby closing the connection between line pressure in line234 and passage 322 and connecting passages 234 and 278. Overdrive brake74 is engaged through operation of accumulator 260. In this way, coastclutch shift valve 302 will not supply pressure to the coast clutch evenif SOL4 pressure is available at the control port of coast clutchpassage 326. In making the upshift from third gear manual to fourthgear, SOL4 pressure is removed permitting the valve 390 to close passage322 and to connect coast clutch 22 to vent port 390.

3. Shift Solenoid Control

A schematic diagram of the driveline, with which the system of thisinvention is used, is shown in FIG. 6. Crankshaft 10 of engine 11 isdrivably connected by torque converter 26 to transmission input shaft38. The rotational speed of the engine is NE, its filtered speed isNEBART, and the speed of output shaft 12 is NO. The crankshaft isdirectly connected to a torque converter impeller 28, whichhydrodynamically drives the torque converter turbine 30. The impeller isselectively connected mechanically to the turbine by operation of torqueconverter lockup clutch 54, whose engagement directly connects theimpeller and turbine mechanically and whose disengagement disconnectsthem mechanically but permits a hydrodynamic connection.

The torque converter speed ratio, SR=NI/NE, is 1:0 when clutch 54 isengaged. The ratio of output shaft speed to vehicle speed is the NOV orN/V ratio. That ratio varies according to the gear ratio of thedifferential mechanism, or axle ratio, and the wheel and tire diameter.The control calculates actual N/V by dividing measured vehicle speed byNO. A base N/V value, stored in computer memory, represents apredetermined axle ratio and tire size. Output shaft speed NO iscalculated, with the torque converter locked, by dividing engine speedby current gear ratio. The transmission gear ratio RG=NI/NO.

The output shaft is drivably connected to a differential mechanism 400,which drives right-hand and left-hand axle shafts 401, 402 and drivewheels 403, 404 of the vehicle.

FIG. 7 illustrates the arrangement of an electronic digital controlsystem that operates on-off shift solenoids SS1, SS2, 188, 190,respectively, converter clutch solenoid on/off valve 192, coast clutchsolenoid on-off valve 194, and variable force solenoid 172, which drivesassociated valve 166 when a pulse width modulated signal is applied tothe winding of solenoid 172.

The electronic control system includes a large scale integrated centralprocessing unit 405; a clock pulse; interval count-down and count-uptimes; read-only memory ROM 406, in which programs controlling thelogical operation of the CPU and data are permanently stored; read-writememory RAM 408; input signal conditioning circuits, for convertinganalog output of various sensors to digital form for processing by theCPU; and solenoid driver circuits 412 for converting digital output ofthe CPU to analog voltage or current supplied to the windings of thesolenoids. An example of a suitable output conditioning circuit forvariable force solenoid 172 is described in U.S. Pat. No. 4,487,303.

Sensors that produce input data to the microprocessor include enginespeed sensor 413, which produces a square wave voltage output having afrequency proportional to the speed of crankshaft 10; temperaturesensors 414, which sense engine coolant temperature and that of anothermedium, such as the transmission fluid, by detecting an electricalresistance that varies with the temperature of the sensed medium;manifold pressure Map sensor 415, which produces a signal representativeof static pressure in the engine intake manifold 702 downstream ofthrottle valve 704, in FIG. 10; throttle position sensor 416, whichproduces a signal representing the degree to which the engine throttleis open or the accelerator pedal is depressed by the vehicle operator inrelation to a reference position; vehicle speed sensor 417, whichproduces a voltage output signal having a frequency proportional to NO,the speed of output shaft 12; sensor 418, which produces an electricalsignal representing the applied or released state of the brake pedal;PRNDL sensor 419, which produces a linear voltage output whose magnitudevaries with the position of the gearshift selector between 0 and 5 voltsand is converted to a binary digit PDL; and overdrive cancel button 420,activated by the vehicle operator, permits or prevents, depending uponthe state of the button, operation of the transmission in overdrivegear, i.e., the fourth forward gear.

FIG. 8 shows data boundaries, defined by vehicle speed VS and TP REL,which corresponds to output produced by throttle position sensor 416indicating the amount of throttle movement from the closed throttle oridle setting, where gearshifts, both upshifts and downshifts, are madeautomatically among the forward gears. Large values of TP REL occur nearwide open throttle WOT, smaller values of TP REL indicate part throttlePT, and values near zero occur near closed throttle CT. The data of FIG.8 are stored in RAM in the form of tables. The transmission gearaccording to the schedule of FIG. 8 is produced from memory using TP andVS as input. As VS and TP REL change during vehicle operation in a givengear such that a line of FIG. 8 is crossed during a background pass froman operating condition defined by these variables in the previous pass,need for a gearshift is indicated following a comparison of the gearfrom the table and the current gear. For example, if the currentoperating condition (first gear) passes from below the 1-2 line to abovethat line, a gearshift from first gear to second gear is commandedbecause of the inequality with the gear from the schedule (second gear),provided other criteria considered by the control so permit. Similarly,downshifts may be commanded when the current operating condition passesthrough a downshift line, the dash lines of FIG. 8, from above therelevant downshift line. When the operating condition during the currentbackground pass is located in the zone between adjacent upshift anddownshift lines, no gearshift is commanded.

Gearshifts are made also on the basis of engine speed corresponding to aWOT condition above which an upshift is commanded regardless of TPvalue. As FIG. 8 indicates, a 1-2 upshift occurs at engine speed NE12S,the shift point at sea level, provided TP is equal to or greater than apredetermined wide open throttle TP. Each of the other upshift lines,2-3 and 3-4, has a corresponding WOT shift point, NE 23S and NE34S. TheWOT shift points are reached before shift points defined by the VS-TPrelationship.

Calibration constants are data stored in RAM accessible to themicroprocessor solely by reference to their memory addresses. Datastored in RAM or other electronic memory in the form of values of afirst variable X, each X value having a single corresponding value of asecond variable Y recalled from memory by reference to a memory locationand the first variable, are f(x) or "fox" functions. Data stored in RAMor other electronic memory in the form of multiple first variables X andY, each combination thereof having a corresponding third variable Z,whose value is recalled from memory by reference to a memory locationand variables X, Y, are called "tables". Data recalled from tables andfox functions are automatically interpolated to correspond to the valuesof the variables used to recall the data. A "register" is a variablewhose value is calculated through execution of algorithms comprising thecontrol.

As FIG. 9 shows, solenoids are controlled by repetitively executingbackground passes whose duration increases with engine speed from about25 msec at idle speed to about 100 msec at high speed. During eachbackground pass, control algorithms divided into modules are executed.The modules are executed serially in the order they are stored in ROM orwhen called from other modules. Each background pass begins afterinitializing various registers, upon reading current input data producedby the sensors, and after storing prior input data acquired during thelast background pass. Shift solenoids SS1, SS2 are controlled by settingflags FLG SS1 and FLG SS2 at ON or OFF states to produce and to preventproduction of SOL1 and SOL2 pressure in any of four possiblecombinations after determining the commanded gear GR CM from the desiredgear DES GR as explained below.

The desired gear is determined on the basis of the gear selectorposition. The following table shows correspondence between commandedgear GR CM, operating state of the transmission, current gear GR CUR,and position PRD of the PRNDL gear selector for each transmission gear.

    ______________________________________                                        GR CM    Transmission State                                                                            GR CUR   PRD                                         ______________________________________                                        1        1st             1        1                                           1.5      2nd, band 102 ON                                                                              2        2                                           2        2nd, band 102 OFF                                                                             2        2                                           3        3rd             3        3                                           4        4th             4        4                                                    Neutral                  5                                                    Reverse                  6                                                    Park                     7                                           ______________________________________                                    

With the gear selector in Drive or Overdrive position, desired gear iscalculated on the basis of a maximum, wide open throttle speed, WOT RPM,shift point or as a function of throttle position TP REL versus vehiclespeed VS. All shift points, whether determined by WOT RPM or by TP vsVS, are adjusted for altitude in accordance with barometric pressure. Astrategy for correcting for barometric pressure or a reference speed,such as vehicle speed or engine speed at which a change in transmissionoperation occurs, e.g. an upshift or downshift, is described withreference to FIG. 11. First, at 421, the current throttle position TPand manifold pressure produced by sensors 416 and 415, respectively, andengine speed NE are read and stored. Sensor 415 is located on the engineintake manifold 702 downstream from the throttle valve 704.Alternatively, the barometric pressure sensor 422 located in the intakemanifold upstream from the throttle valve could be used. At 423, thereference speed at which a change in operation of the transmission is tooccur is determined by referring to the gearshift schedule of FIG. 8stored in electronic memory. The reference speed can be engine speed orthe vehicle speed depending upon whether the gear change is made on thebasis of wide open throttle condition or a VS-TP.

At 424, barometric pressure in digital form is converted from the signalproduced by sensor 415 to produce inferred barometric pressure byemploying data stored in RAM, as illustrated in FIG. 13. The data ofFIG. 13 is stored as a lookup table of barometric pressure correctionvalues corresponding to throttle position TP, the vertical axis, andengine speed, the horizontal axis NE. Although the table of FIG. 13includes values only at the extremities of the ranges of independentvariables used as input to produce the pressure increments, in fact theentire table is filled with data, so that barometric pressure can beinferred from the output of sensor 415. If an ambient barometric sensornot affected by its location downstream of the throttle valve is used,such as sensor 422, barometric pressure need not be inferred but can beused directly from the output of that sensor. The data of table 13results from an ambient reference barometric pressure, for example,barometric pressure at sea level.

Next, memory locations where the fox function of FIG. 14 is stored arereferenced having as input the current throttle position TP to produceas output a difference in reference speed at which the operationalchange of the transmission is to occur. For example, if the change is awide open throttle 1-2 upshift, a speed difference NE12A is retrievedfrom memory. If a 3-4 upshift is to be produced on the basis of thevehicle speed schedule of FIG. 8, the fox function represented by FIG.14 produces a speed difference FN34A. The speed difference values of therelevant fox functions are determined preferably at high altitudeambient barometric pressure.

At 426 a barometric pressure interpolation factor BPINTR is determinedfor the inferred barometric pressure from the data represented in FIG.15. The interpolation factor varies over a range of approximately 0-2.0and increases in magnitude as inferred barometric pressure decreasesfrom its maximum. At or near the altitude where the fox functionrepresented by FIG. 14 is established, the barometric pressureinterpolation factor is approximately 1.0 and remains constant althoughinferred barometric pressure decreases. Thereafter, the interpolationfactor again increases to a maximum value and remains constant despitedecreasing inferred barometric pressure. The computer controlautomatically interpolates and determines the current BP INTR factorfrom the current ambient barometric pressure value produced as input bysensor 416.

At 427, the reference speed where the operational change is commanded iscalculated to correct for current barometric pressure using theequations stated in box 427. After the shift point speed is determinedin this way, at 428 an inquiry is made to determine whether thereference speed for the operational change is equal to or greater thanthe reference speed corrected for the current ambient barometricpressure. If the reference speed, for example, NE or VS, exceeds thealtitude corrected reference, the inquiry is true and control passes tostatement 429 where a command that will result in a change oftransmission gear is made by setting register gear command GR CM equalto 2 or 3, depending upon whether the gear ratio change is made inresponse to the wide open throttle condition or to vehicle speedcondition used here as examples.

If inquiry 428 is false, at 430 the current command gear is maintainedbecause no change in operating condition is required. After statement429 or 430 is executed, the shift solenoid state module is called atstatement 431.

Although the wide open throttle shift point described with reference toFIG. 11 is for a 1-2 upshift and the vehicle speed scheduled shift pointhas been described with respect to a 3-4 upshift, upshifts anddownshifts for either scheduled or wide open throttle conditions can bemade among any of the gears of the transmission. Also, the change inoperation can be other than a gearshift, e.g., a change in state of thetorque converter clutch.

An example of applying the barometric pressure correction technique isdescribed next for upshifts and downshifts.

Vehicle Speed Sensor OK Shift Module--FIGS. 12a-12c

This module begins at statement 446 where current gear is compared tofirst gear. If that comparison is true, a comparison is made at 447 todetermine whether engine speed NE is above wide open throttle speedcorresponding to the 1-2 shift point corrected for altitude. NE is thefiltered engine speed during the current background pass. NE12S is thewide open throttle speed at sea level where the 1-2 shift occurs. BPINTR, an interpolation factor corresponding to barometric pressure atthe current altitude of the vehicle produced by sensor 415, ismultiplied by NE12A, the wide open throttle engine speed difference atthe current altitude where the 1-2 shift point occurs. If current enginespeed is above the engine speed for the 1-2 shift point corrected foraltitude, statement 448 is executed, whereby desired gear is set equalto 2 indicating second gear, and flag FLG UP NE is set to indicate thatthe upshift is due to a wide open throttle condition.

If 446 is true, a comparison is made at 447 to determine whether enginespeed is above wide open throttle speed for the 1-2 shift pointcorrected for altitude. To make this comparison, engine speed iscompared to the speed resulting from the sum of NE12S, a calibrationconstant stored in computer memory defining the engine speed above whichan upshift from the first gear to the second gear occurs at sea level,and the product BP INTR * NE12A. BP INTR is an interpolation factorstored in computer memory as a f(x) function related to a range ofambient barometric pressure values X. NE12A is a calibration constantstored in computer memory containing a predetermined engine speed bywhich the shift point at sea level is altered to account for altitudedifference. This speed difference is multiplied by BP INTR and theproduct is added to the sea level shift point engine speed.

If both statements 446 and 447 are true, desired gear is set equal to 2and a flag is set to indicate an upshift due to a wide open throttlecondition is desired. However, if either statement 446 or 447 is false,an inquiry is made at 449 to determine whether second gear is thecurrent gear and, if so, at 450 whether engine speed is above the wideopen throttle shift point corrected for altitude, as has been describedfor a 1-2 upshift with respect to statement 447. If statements 449 and450 are true, desired gear is set to 3 and wide open throttle upshiftflag FLG UP NE is set.

Thereafter, desired gear is determined on the basis of vehicle speedrather than engine speed. If either statement 449 or 450 is false, at451 a comparison is made to determine whether current gear is equal toor greater than third gear. If so, at 452, the current vehicle speed VSis compared to an altitude corrected VS for a 3-4 upshift. The value tobe compared to vehicle speed includes the variables: FN34S, acalibration constant vehicle speed where a 3-4 upshift at sea level ismade; BP INTR, the barometric pressure integration factor; FN34A, acalibration constant stated in terms of vehicle speed differencerepresenting a correction of vehicle speed at sea level where a 3-4upshift is made; RT NOVS, the ratio of calculated N/V to a base orcalibration constant N/V stored in keep-alive memory KAM; and CS SFTMULT, a cold start shift multiplier. If statements 451 and 452 are true,and if PDL is equal to 4, desired gear is set equal to 4. CS SFT MULTvaries between 1.0 when transmission fluid temperature is warm and 1.25when it is cold. Its value also depends on the fluid temperature atstart-up.

The desired gear is set equal to 3 if either statement 451 or 452 isfalse, current gear is less than 3, and vehicle speed is above analtitude corrected VS for an upshift to third gear.

If either statement 454 or 455 is false, a comparison is made at 456 todetermine if the current gear is less than 2 and, at 457, to determinewhether vehicle speed is above altitude corrected VS for an upshift tosecond gear. If both of these conditions are true, desired gear is setequal to 2.

The control continues thereafter with respect to downshifts in a similarway. For example, at 458 current gear is compared to 1, and at 459vehicle speed is compared to an altitude corrected vehicle speed for a2-1 downshift. The interpolation factor, calibration constants, andother variables shown in the equation at statement 459 are the same asthose discussed previously with respect to statement 452 except that thecalibration constants relate to a 2-1 downshift rather than a 3-4upshift.

If statements 458 and 459 are true, desired gear is set equal to 1;however, if either of these statements is false, at 460 a comparison ismade to determine whether the current gear is greater than 2. If so, at461 the comparison is made to determine whether vehicle speed is belowaltitude corrected vehicle speed for a downshift to the second gear, andif true, desired gear is set equal to 2.

If statement 460 or 461 is false, a comparison is made at 462 todetermine whether a current gear is greater than 3, and, if so, whethervehicle speed is below altitude corrected vehicle speed for a downshiftto third gear. If statements 462 and 463 are true, desired gear andcurrent gear are set equal to 3 and execution of the module terminates.If statements 462 or 463 are false, a comparison is made at 464 todetermine whether current gear is greater than 3, and, if so, whetherthe operator has moved the PRNDL gearshift lever to the 3 position,thereby indicating that a manual downshift is desired. If a manualdownshift is desired, both current gear and desired gear are set equalto 3; otherwise, only current gear is set equal to 3 and executionpasses to the shift solenoid state module.

Shift Solenoid States Module--FIG. 20a-20b

The shift solenoid state module establishes the shift solenoid outputstates on the basis of commanded gear. The shift solenoids havedifferent reaction rates, e.g., the solenoid that operates shift valve188 reacts faster than the solenoid that operates shift valve 190. Gearshift changes are made for changing the state of only one shiftsolenoid, except when PRNDL movement causes a commanded gear change from1.5 to 2. When this occurs, both shift solenoids move from off-state toon-state. A countdown timer is set when this condition occurs so thatsolenoid SS2, which operates shift valve 190, is energized beforesolenoid SS1 so that both hydraulic shift valves move to the on-state atthe same time.

At 520 a comparison is made to determine if first gear is the commandedgear. At 522, if comparison 520 is true, shift solenoid SS1 is energizedand shift solenoid SS2 is deenergized. The gear ratio corresponding tofirst gear is set equal to register SPD RT ST RT, which is the speedratio at the beginning of the shift, and the current gear is set equalto 1. If comparison 520 is false, comparison 524 is made to determinewhether second gear with the intermediate band ON is the commanded gear.If so, shift solenoids SS1 and SS2 are deenergized and SS1 delay timeris loaded with a predetermined time to allow SS2 to move prior to SS1because of the difference in response times previously referred to. Thenthe gear ratio is set equal to the second gear ratio and current gear isset equal to 2.

If comparison 524 is false, comparison 528 is made to determine whethersecond gear with the intermediate band OFF is the commanded gear andwhether SS1 delay timer has expired. If so, the statement represented by530 deenergize SS1, energize SS2, sets the gear ratio to the secondgear, and sets current gear equal to 2.

If the comparison at 528 is false, statement 532 determines whethersecond gear with intermediate band OFF is the commanded gear. Thiscondition implies that SS1 delay timer is expired. Then both shiftsolenoids are energized, and the gear ratio and current gear are setequal to corresponding second gear values.

A comparison is made at 536 to determine whether third gear is thecommanded gear. If it is, solenoid SS1 is deenergized and SS2 isenergized, the gear ratio and current gear are set equal to third gearvalues. If the comparison at 536 is false, a final comparison at 540determines whether fourth gear is the commanded gear. Statement 542causes the shift solenoids SS1 and SS2 to be deenergized and the fourthgear values to be set equal to current gear and gear ratio.

After statements 522, 526, 530, 534, 538 and 542 are executed, or if thecomparison at 540 is false, control moves to a comparison at 544 todetermine whether a shift is commanded during the current backgroundpass. If so, the speed ratio at the start of the shift is set equal tothe value specified in statement 546. When this is done, or if thecomparison at 544 is false, execution of this module terminates.

4. Torque Converter Control--FIG. 16

After the control is enabled, usually upon staring the engine,background passes execute sequentially but with interrupts that occur at1 msec intervals. Engine timing pulses occur at the rising edge orfalling edge of a square wave whose period is proportional to the numberof engine cylinders, kind of engine and engine speed. For example, whenthe powertrain of FIG. 6 includes an eight cylinder, four stroke engine,at 6000 rpm the period DT12S between these pulses expressed in clockpulses between each rising edge is 2.5 msec (60 sec. per min./4 pulsesper rev./6000 rpm). After each pulse, certain functions necessary tooperate the vehicle are executed under the control of algorithms, calledand executed upon occurrence of each timing pulse. After each of thesepulses, functions are commanded and executed, and data produced byvarious sensors are read, converted to digital form, and storedelectronically for use later in calculations and control logic.

The frequency at which the timing pulses occur varies with engine speed,but certain data are required to be read, updated and processed morefrequently. For example, during a power-on upshift, such as thatdiscussed below with reference to FIG. 21, torque converter speed ratiois calculated during each interrupt and its current value is compared toa predetermined value.

In vehicles having front wheel drive, space limitations and lack ofaccess to certain transmission shafts require that no torque converterturbine speed sensor be used. But converter speed ratio SR is required.Instead, torque converter turbine speed NI is calculated from currentvehicle speed and current transmission gear, for which the associatedgear ratio is a stored constant value. Vehicle speed is known from dataproduced by sensor 417. Turbine speed NI is calculated from NO and thegear ratio. Converter speed ratio SR is equal to NI/NE.

The technique can be understood best with reference to FIG. 16. Enginespeed varies with time as transmission gear ratio changes are made, butVS is assumed to be, and is in fact, substantially constant during eachbackground pass. When engine speed rises to A in FIG. 21, an upshift,e.g. a 2-3 upshift to third gear, is commanded.

At B, the oncoming function begins to engage. The control logic,immediately after occurrence of an upshift command and thereafter untila new commanded gear issues, uses third gear as the current gear in allsubsequent calculations. However, a short period passes between thecommand to produce third gear and its completed engagement. Aftercurrent gear acquires its third gear value upon issuance of the upshiftcommand, calculated torque converter speed ratio SR falls, as in FIG.21, from 1.00, the value corresponding to the converter lockup clutchbeing engaged, to a lower value, e.g., 0.70. This reduction occursbecause impeller speed NI, calculated on the basis of the new gear ratiofor third gear, is lower than NI for second gear assuming vehicle speedis constant. The lower calculated SR value is inaccurate until theupshift is completed at F, where calculated and actual speed ratio areagain 1.00.

During the interval from A to F, SR rises from 0.70 to 1.00 as theoncoming and off-going friction elements attain the status each has atcompletion of the upshift, and the converter clutch relocks. At time C,the control issues a command which unlocks converter clutch 54. At timeD, the control issues a command to relock the converter, and the relockis completed at time F. During the D-F period, the gear ratio change iscompleted at E where the oncoming friction element becomes fullyengaged.

At time C and thereafter, continuously during the period before clutch54 is relocked at F, converter SR rises as NE falls due to progressiveengagement of the oncoming friction brake or clutch and the associatedgear ratio reduction this engagement produces. During the A-F period,current converter SR must be compared to predetermined reference speedratios to establish time C, when clutch 54 is commanded unlocked, andtime D, when the clutch is commanded relocked. Converter SR changes toofast during the A-F period to maintain control if the comparison isperformed only once per background pass. Therefore, a comparison is madeduring each 1 msec interrupt between reference unlock and referencerelock converter speed ratios to determine when to unlock and relock theconverter clutch. The converter speed ratio is proportional to the ratioNE/VS. The speed ratio at C and D, where the converter unlocks and laterrelocks, are known.

To implement this control strategy for the torque converter, a registerSR LIM is calculated in units of clock pulses. It represents thereference unlock torque converter speed ratio and, at a later pointduring the execution of the control algorithm, the reference relocktorque converter speed ratio. SR LIM is determined once per backgroundloop and is compared to DT12S, which is the number of clock pulsesproduced by the internal clock of the microprocessor control unitbetween the rising edges of the square wave timing pulses produced bywave generator 407. The reference speed ratio is related to engine speedand is expressed in units of clock pulses. Rapid changes in converterspeed ratio are determined each millisecond during the interrupt. DT12Sis updated at that frequency and compared at that frequency to thereference converter speed ratio, which is updated once per backgroundloop.

After the converter clutch control begins to operate and the comparisonshows that DT12S exceeds SR LIM, a command to unlock clutch 54 issues.Next, a new value for SR LIM corresponding to a higher converter speedratio, at which the converter clutch is to relock, is calculated. WhenDT 12S again equals or exceeds the new reference speed ratio, a commandto relock the clutch issues. Commands to unlock and relock the clutchcause converter solenoid SOL3 to change state, which action causes valve192 to change state and produce the desired change in the state ofclutch 54. If the calculated converter speed ratio does not reach orexceed the reference speed ratio before expiration of a default timerset to regulate the length of the period between the commands to lockand relock the converter and their execution, then clutch 54 isimmediately locked and relocked upon expiration of the timer.

Vehicle speed, updated each background pass, is known from outputproduced by sensor 417, and is equal to the product of the following:engine speed NE, known from the output of sensor 413; transmission gearratio RG, available from electronic memory as a stored constant; NOV,the ratio NO/VS; and torque converter speed ratio, for which no sensorinformation is available directly. However, because all of the othervalues of this relationship are known, torque converter speed ratio canbe calculated from VS/NE*RG*NOV. In this way, the reference converterspeed ratio SR LIM is calculated and updated once per background loop,the first calculation being made with the gear ratio corresponding tothe desired gear in which the transmission is to operate at theconclusion of the gearshift change.

An example of this is third gear set at time A for the 2-3 upshiftdescribed with reference to FIG. 16. Using this example, the initialreference converter speed ratio is 0.7 at time A. Stored in memory asfox functions of throttle position and desired gear are converter speedratio unlock correction factors SRDU, an example of which is shown inFIG. 17. The initial reference speed ratio is updated by adding SRDU toestablish the unlock reference speed ratio, 0.73 in FIG. 16, at whichthe converter clutch is unlocked. By suitably adjusting the dimensionalunits, this value is expressed in terms of clock pulses corresponding tothe dimension of DT12S.

After clutch 54 is unlocked, the converter reference speed ratio isupdated again recalling from computer memory on the basis of currentthrottle position, a relock converter speed ratio correction SRDR. Thissecond correction is added to the reference speed ratio to produce aspeed ratio that is compared to the rapidly changing value DT12S. Whentorque converter speed ratio, expressed in clock pulse units, equals orexceed the relock reference speed ratio, a command issues to relock thetorque converter clutch.

Converter unlock and relock timers are set when the correspondingcommands to change the state of clutch 54 issue. Upon expiration of thetimers, the converter clutch is unlocked and relocked regardless of theresult of the comparison of current converter speed ratio with thereference speed ratio.

Converter Clutch Control Module--FIG. 19

An example of the technique for controlling converter clutch during agear ratio change is described next with reference to FIG. 19. At 466,an inquiry is made to determine whether the torque converter is lockedand, at 467, whether a gearshift is commanded. If either statement 466or 467 is false, execution of the module terminates, but, if bothstatements are true, control passes to 468 where engine speed, vehiclespeed NOV and gear ratio RG for the commanded gear are read orcalculated. From values determined by executing statement 468, thecurrent torque converter speed ratio is calculated by executing 469. At470, a converter unlock countdown timer is set with a predeterminedperiod that unlock clutch 54 when the timer expires.

At 471, a converter clutch unlock speed ratio increment SRDU, recalledfrom computer memory on the basis of current throttle position, is addedto the calculated converter speed ratio to produce SRU, the referenceconverter unlock speed ratio. At statement 472, SRU is converted to SRLIM, the unlock converter speed ratio reference in units of clock pulsesper timing pulse. This value is comparable to the number of clock pulsesrepresented by DT12S, which is upgraded each millisecond during a highspeed interrupt 473.

At 474, a comparison is made to determine whether DT12S is equal to orgreater than SR LIM. If statement 474 is true, at 475, flag FLG LK CM isset equal to zero, thereby deenergizing the converter clutch solenoidSOL3 and causing the pressure output from valve 192 to release theconverter clutch. If statement 474 is false, an inquiry is made at 476to determine whether the unlock timer has expired. If so, 475 isexecuted, but if not, control passes to 474 to determine whether thevalue of DT12S, updated during the next high speed interrupt, hasattained a value that permits clutch 54 to unlock. This loop continuesuntil either the timer is expired or the speed ratio criteria issatisfied.

Thereafter, at 482, SRDR is recalled from memory on the basis of currentthrottle position. This value is added to the reference converter clutchspeed ratio to produce SRR, the converter relock speed ratio. SRR isconverted to SR LIM, the relock reference in clock pulses per timingpulse, by the equation in block 472.

At 477, a torque converter relock countdown timer is set at apredetermined speed. Successive high speed interrupts 478 continue atone millisecond intervals.

At 479, an inquiry similar to that at 474 is made to determine whetherDT12S equals or exceeds the relock reference speed ratio SR LIM. Ifstatement 479 is true, at 480, converter clutch solenoid SOL3 isenergized by setting the command flag FLG LK CM equal to 1 so thatpressure output from valve 192 causes clutch 54 to relock. If statement479 is false, at 481, a check is made to determine whether the relocktimer has expired. If expired, statement 480 is executed, but ifunexpired, control passes again to statement 479. This relock loopcontinues to update DT12S until DT12S equals or exceeds the current SRLIM or the relock timer expires. Thereafter, clutch 54 is relocked.

Having described a preferred embodiment of our invention, what we claimand desire to secure by U.S. Letters Patent is:
 1. A method forcontrolling gearshifts in an automatic transmission of a motor vehiclehaving an engine, electronic computer, electronic memory accessible tothe computer, comprising:generating an engine speed signal; storing inmemory engine speeds corresponding to a wide open throttle condition atwhich gearshifts are scheduled to occur at a reference barometricpressure; calculating a engine speed barometric pressure correction toaccount for a difference between reference barometric pressure andcurrent ambient barometric pressure; generating, in response to theengine speed barometric pressure correction, an altitude correctedengine speed signal representing engine speed corresponding to a wideopen throttle condition at which gearshifts are to occur at currentambient barometric pressure; comparing the current engine speed signalto the barometric pressure corrected engine speed signal; and producinga gearshift when the comparison indicates current engine speed exceedsthe barometric pressure corrected engine speed.
 2. A method forcontrolling upshifts in an automatic transmission of a motor vehiclehaving an engine, electronic computer, electronic memory accessible tothe computer, comprising:generating an vehicle speed signal and athrottle position signal; storing in memory a upshift schedule ofoperating conditions defined by vehicle speed and throttle position atwhich conditions upshifts are scheduled to occur at a referencebarometric pressure; calculating a vehicle speed barometric pressurecorrection to account for a difference between reference barometricpressure and current barometric pressure; generating an altitudecorrected vehicle speed signal, in response to the vehicle speedbarometric pressure correction, at which upshifts are to occur atcurrent barometric pressure; comparing the current engine speed signalto the barometric pressure corrected engine speed signal; and producinga upshift when the comparison indicates current vehicle speed exceedsthe barometric pressure corrected vehicle speed.
 3. A method forcontrolling downshifts in an automatic transmission of a motor vehiclehaving an engine, electronic computer, electronic memory accessible tothe computer, comprising:generating an vehicle speed signal and athrottle position signal; storing in memory a downshift schedule ofoperating conditions defined by vehicle speed and throttle position atwhich conditions downshifts are scheduled to occur at a referencebarometric pressure; calculating a vehicle speed barometric pressurecorrection to account for a difference between reference barometricpressure and current barometric pressure; generating an altitudecorrected vehicle speed signal, in response to the vehicle speedbarometric pressure correction, at which downshifts are to occur atcurrent barometric pressure; comparing the current engine speed signalto the barometric pressure corrected engine speed signal; and producinga downshift when the comparison indicates current vehicle speed is lessthan barometric pressure corrected vehicle speed.
 4. A system forcontrolling gearshifts in an automatic transmission for a motor vehiclehaving an engine, electronic computer, electronic memory accessible tothe computer, comprising:means for generating an engine speed signal;means for storing in memory engine speeds corresponding to a wide openthrottle condition at which gearshifts are scheduled to occur at areference barometric pressure; means for calculating a engine speedbarometric pressure correction to account for a difference betweenreference barometric pressure and current ambient barometric pressure;means responsive to the engine speed barometric pressure correction forgenerating an altitude corrected engine speed signal representing enginespeed corresponding to a wide open throttle condition at whichgearshifts are to occur at current ambient barometric pressure; meansfor comparing the current engine speed signal to the barometric pressurecorrected engine speed signal; and means producing a gearshift when thecomparison indicates current engine speed exceeds the barometricpressure corrected engine speed.
 5. The system of claim 4 furthercomprising:means for storing in memory engine speed calibrationconstants corresponding to upshifts at a wide open throttle condition;means for storing in memory barometric pressure interpolation factors,each factor corresponding to a current barometric pressure over a rangeof current barometric pressures; means for determining the current gearand the current barometric pressure; means for recalling from memory theengine speed calibration constants corresponding to a wide open throttlecondition and an upshift from the current gear; means for recalling frommemory and determining the interpolation factor corresponding to thecurrent barometric pressure; and means for calculating a engine speedbarometric pressure correction to account for a difference betweenreference barometric pressure and current barometric pressure from theengine speed calibration constant and the interpolation factorcorresponding to the current barometric pressure.
 6. A system forcontrolling upshifts in an automatic transmission for a motor vehiclehaving an engine, electronic computer, electronic memory accessible thecomputer, comprising:means for generating an vehicle speed signal and athrottle position signal; means for storing in memory a upshift scheduleof operating conditions defined by vehicle speed and throttle positionat which conditions upshifts are scheduled to occur at a referencebarometric pressure; means for calculating a vehicle speed barometricpressure correction to account for a difference between referencebarometric pressure and current barometric pressure; means responsive tothe vehicle speed barometric pressure correction for generating analtitude corrected vehicle speed signal at which upshifts are to occurat current barometric pressure; means for comparing the current enginespeed signal to the barometric pressure corrected engine speed signal;and means producing a upshift when the comparison indicates currentvehicle speed exceeds the barometric pressure corrected vehicle speed.7. The system of claim 3 further comprising:means for storing in memorya vehicle speed calibration constants corresponding to each upshift inthe stored upshift schedule; means for storing in memory barometricpressure interpolation factors, each factor corresponding to a currentbarometric pressure over a range of current barometric pressures; meansfor determining the current gear and the current barometric pressure;means for recalling from memory a vehicle speed calibration constantcorresponding to an upshift from the current gear; means for recallingfrom memory and determining the interpolation factor corresponding tothe current barometric pressure; and means for calculating a vehiclespeed barometric pressure correction to account for a difference betweenreference barometric pressure and current barometric pressure from thevehicle speed calibration constant and the interpolation factorcorresponding to the current barometric pressure.
 8. A system forcontrolling downshifts in an automatic transmission of a motor vehiclehaving an engine, electronic computer, electronic memory accessible tothe computer, comprising:means for generating an vehicle speed signaland a throttle position signal; means for storing in memory a downshiftschedule of operating conditions defined by vehicle speed and throttleposition at which conditions downshifts are scheduled to occur at areference barometric pressure; means for calculating a vehicle speedbarometric pressure correction to account for a difference betweenreference barometric pressure and current barometric pressure; meansresponsive to the vehicle speed barometric pressure correction forgenerating an altitude corrected vehicle speed signal at whichdownshifts are to occur at current barometric pressure; means forcomparing the current engine speed signal to the barometric pressurecorrected engine speed signal; and means producing a downshift when thecomparison indicates current vehicle speed is less than barometricpressure corrected vehicle speed.
 9. The system of claim 8 furthercomprising:means for storing in memory a vehicle speed calibrationconstants corresponding to each downshift in the stored gearshiftschedule; means for storing in memory barometric pressure interpolationfactors, each factor corresponding to a current barometric pressure overa range of current barometric pressures; means for determining thecurrent gear and the current barometric pressure; means for recallingfrom memory a vehicle speed calibration constant corresponding to andownshift from the current gear; means for recalling from memory anddetermining the interpolation factor corresponding to the currentbarometric pressure; and means for calculating a vehicle speedbarometric pressure correction to account for a difference betweenreference barometric pressure and current barometric pressure from thevehicle speed calibration constant and the interpolation factorcorresponding to the current barometric pressure.